A suicide bomber has attacked a Nato military convoy in the southern Afghan province of Helmand, killing two Danish soldiers and a Czech soldier.
There has been an increase in attacks in recent months
Police say an Afghan interpreter was also killed. Correspondents say that there are conflicting reports as to whether civilians were also killed.
Earlier reports said some civilians were killed in the blast in the district of Gereshk.
There has been a sharp increase in violence in Afghanistan this year.
Suicide bombs are increasingly common.
The BBC'S Alastair Leithead says that the Nato troops were on patrol when they were attacked by the suicide bomber, who was on foot.
An eyewitness told the BBC the man was young and had detonated his explosive vest among the soldiers, who were not in vehicles.
The spokesman for the Helmand Task Force, Lt Col Simon Millar, said that the three soldiers who died all worked to co-ordinate civilian and military aid.
Our correspondent says that there are conflicting reports of civilian casualties.
Nato and one local official say six people were injured. But the police chief says that three were killed.
Insurgents have been increasingly using suicide and roadside bomb attacks to target international and Afghan security forces.
More than 450 international troops have died in Afghanistan since the beginning of 2006 - Nato has also confirmed that a Canadian soldier was killed on Sunday while on a foot patrol in neighbouring Kandahar province.
Last week, six people were killed and at least 15 injured in a car bomb attack on a coalition convoy near the airport in the capital, Kabul.
In February a car bomb in the southern city of Kandahar killed more than 100 people. It was the worst single attack since the fall of the Taleban in 2001.
A UN report published this week said there were 8,000 conflict-related deaths in 2007 - a fifth of which were civilians.